Merging the mobility of the cellular telephone network with the information capability and accessibility of the Internet has become a main focus of the communications industry. In particular, in recent years considerable research has been directed to developing mobile protocols that would allow seamless access to the multimedia services available on the Internet thereby allowing consumers to be online anytime and anywhere.
The Internet is a packet data network in which the Internet Protocol (IP) defines the manner in which a user is connected to the Internet so as to access, transmit, and receive information from other users or resources connected to the Internet. In particular, in accordance with IP each network access point is identified by an IP address. When a user attaches to a particular network access point the user's terminal or station is given an IP address. Access points addresses are assigned geographically. Consequently, as a user roams geographically the user's terminal point of attachment to the network changes which in turn requires the terminal's IP address to change. Further, information destined for a user, or resource, is packetized with each packet having the IP address of the user's terminal in a header. As packets traverse the network, the IP address included in the header is used to route the packet to its destination. Thus, as a user roams and her terminal's IP address changes, the route to the user changes which in turn may affect the quality of service for some multimedia services, i.e., real time services, as there is no guarantee that network resources required to support the service are available. At a fundamental level IP was not designed with mobility in mind as evidenced by the manner in which IP addresses are assigned.
In contrast, the cellular or wireless telephone network is a circuit switched network with each user's telephone number serving as a unique access identifier. Consequently, as the user roams geographically the user's identity is unchanged thereby allowing the network to easily track the user's movement, establish new circuits in anticipation of the user moving to a different geographic region, and maintain the needed quality of service. In addition, in the wireless telephone network calls between users are routed through the network on circuits that are established for the duration of the call. In other words, a path is established in the network for exclusively carrying each call thereby assuring the user of the bandwidth needed for the service.
Given the fundamentally different approaches underlying the manner in which access is provided by the Internet and by the wireless telephone network and the manner in which paths are established and signals routed through each of these networks, many issues need to be resolved before multimedia services can be provided over an IP wireless network. More precisely, these issues must be resolved before third generation wireless networks offering mobile multimedia services via an IP platform can become a reality. Of particular import to the present invention is the assignment of IP addresses to user terminals or stations as users move about geographically thereby changing their point of attachment to the network. IP address assignment is an even more vexing problem because of the limited amount of IP addresses available via the current version of IP, IP Version 4 (IPv4).
Specifically, in a wireless network such as shown in FIG. 1, a plurality of base stations 10 transmit or send information over the air to a plurality of mobile units or stations 20. The range within which a mobile unit 20 can reliably receive information from a base station 10 defines a cell 21. As illustrated in FIG. 1 the cells 21 may be depicted as a honeycomb structure. As a mobile unit 202, for example, roams and moves further away from a base station 102 corresponding to cell 212 for base station 102, signal strength decreases. Further, as the mobile moves from one cell to another, the mobile station needs to switch from its serving base station, the base station for the cell it currently is in, to a target base station, the base station for the cell that it's moving to. The process of the mobile switching base stations is known as handoff.
As discussed above, in an IP network IP addresses are assigned geographically. Consequently, in a wireless IP network as a mobile unit moves around and switches base station, the mobile unit may need to be assigned a new temporary IP address. For example, in FIG. 1 base stations 101 and 107 are depicted as being on the same subnetwork or subnet, subnet A. On the other hand, base stations 102 and 104 are on a different subnet, subnet B. Both these subnets are shown as being served by the same router R that is connected to much larger network N. If mobile station 202 is handed off from base station 102 to either base station 101 or 107 the station will change subnets. As is known in the art, whenever a terminal changes IP subnets that terminal will require a new temporary IP address while it remains attached via that subnet. In addition, when the user's terminal moves into a new IP subnet, the terminal may also need to verify the uniqueness of the assigned temporary IP address and perform IP-layer processing.
Today, approaches for an IP terminal to obtain a temporary IP address dynamically include the Point-to-Point (PPP) protocol, the Dynamic Host Configuration Protocol or DHCP, and Mobile IP. An important characteristic shared by today's approaches is that a mobile station or the target base station can start the process of obtaining new IP addresses only after the mobile station moves into the new subnet and establishes a radio connection with the target base station. Consequently, the time it takes to obtain new addresses, to verify the assigned addresses and to perform IP-layer registration becomes extra handoff delay in a wireless network. Such extra handoff delay can often become too long to be tolerable to most real-time applications such as voice and video. For example, lab experiments show that using Dynamic Registration and Configuration Protocol (DRCP) to obtain a new IP address could take over 15 seconds (dominated by the delay of using the Address Resolution Protocol or ARP to verify the uniqueness of the assigned address), which is beyond the tolerable range of end-to-end delay for most real-time applications, such as voice and video services.
IP address conservation appears to be a key reason that today's dynamic address assignment mechanisms assign address only after the unit requesting the address has established radio contact with the target base station. Prior art approaches for dynamic assignment of IP addresses need to conserve IP addresses because the current version of IP, i.e., IP Version 4 or IPv4, is running out of address space. The lack of address space in IPv4 is due to the fact that IPv4 has only a 32-bit field for an IP address. On the other hand, version 6 of IP (IPv6) will include a 128-bit IP address field.
Accordingly, under IPv6 IP addresses will be available in abundance. As such, new methods for dynamic assignment of addresses may be developed that are better suited to support the third generation wireless environment wherein mobile user terminals will often require temporary IP addresses as users roam about. Such new methods should be free of the constraint to conserve IP addresses and will be needed to support third generation wireless real-time multimedia services.